Stress and failure characteristics of surrounding rock in the extremely close distance coal seams group mining after the upper and lower coal seam mining

In response to the engineering specifications of the middle coal seam mining after the upper and lower coal seam mining during the extremely close distance coal seam group mining, by adopting the numerical simulation, analog simulation and the engineering practice, the stress distribution, the displacement variation characteristics and the fracture of the stope surrounding rock during the extremely close distance coal seam mining has been analyzed. Results show that the roof and floor stress decreases, and its integrity isn't badly damaged during the extremely close distance coal seam mining when the coal seam is not thick, the roof and floor rocks are relatively stable and the mining height are about 3 meters. While the surrounding rock stress concentration strengthens significantly at the range of the district sublevel entry outside. It forms a shear fracture zone 35 m near to the open-off cut and terminal line. During the extremely close distance coal seam mining, repair and reinforcement for the two roadways should be strengthened and the working face should be reasonably arranged to avoid the high stress zone and the shear fracture zone. Meanwhile the corresponding underground pressure control measures should be taken, ensuring the working face safety mining.